Electrical apparatus



Feb. 8,1927. 1.617,l78

AAAAAAAAAAAAAAAAA US Patented F eh. 8, 127.

UNTED'STATE PATENT OFFICE- VANNEVAR BUSI E, OF C HEL SEA., MA SSACHUSETTS, ASSIGI'OR, BY MESNE ASSIGN- MENTS, TO RAYTHEON MANUFACTURING COMPANY, OF CAMBRIDGE, MASSACHU- SE'I'TS', A CORPORATION OF MASSACHUSETTS.

ELECTRICAL APPARATUS.

Application filed October 27, 1921. Serial No. 510,916Q

This invention relates to electrical apparatus, such as rectifiers, ofthe type having opposed electrodes between which current flows by gaseous conduction, and more par- 5 ticularly to apparatus having electrodes of the low temperature type, that is, of the type which` operate below thermo'nic emission temperature in contradistinction to the incandescent type, A rectifier of the general class to, which the present invention relates is disclosed in the copending application of Smith, Serial No. 415,536, filed October'S, 1920.

Apparatus of this type operate at relatively high potentials compared to the operating potentials for thermionic tubes, and the consequent positive ion bombardment of the cathode surface, as well as other exposed suro faces in the tube, gives rise to problems which are ordinarily not experienced in thermionic tubes. of preventing the gas molecules from being permanently entrapped by the aforesaid bombardment of positive ions, thereby reducing the gas pressure below that required for norinal operation of the tube. Such occlusion Will ordinarily take place in tubes of the type referred to, both in the solid metal of the electrodes (principally the cathode) and also in the Walls of the glass tube and other surfaces exposed to the bombardment.

[n one aspect this invention involves confining said bombardment to a restricted area, preferably the active surface of the cathode, and in another aspectthejinvention involves forming the bombarded area of material which, instead of entrapping the gas, permits the gas to escape. This is preferably accomplished by making the cathode surface, or other bombarded area, of material which is porous, that is, constituted to permit the gas to escape. While there are yaro'us Ways of preventing the gas from bengentrapped, as disclosed in subsequent appl cations of said Smith, the specific way her-eini after described is to make the bombarded surface of carbon.

In a* more specific aspect this invention involves apparatus in which the spacing between the electrodes and the gas pressure are correlated to prevent substantial conduction along the Shortest paths between the electrodes at potentials which produce gase- One such problem is that ous .conduction along longer paths between the electrodes, n combnaton wth means as aforesad, for preventng the gas from being entrapped, Whereby the gas pressure is maintained in proper relation to the lengths of said paths. Thus the invention afi'ord's a solution for the' problem, which is peculiar to tubes of the type disclosed in said Smith application, of keeping the pressure sufiicient-ly low to prevent eonduction along the short paths while preventing the pressure from becoming too low for conduction along the longer paths, at least at the rated volttions to vary conduction through the gas and cause complete rectification if so desrcd.

As conducton between electrodes of this character takes place by virtue of ioization of the gas rather than by thernionic condueton a Vav or by arcng between the electrodes, it is lighly desirable that the 4 claracte'istivs of the gaseos mediun in which the electrodes are innersed shall remain snbstantially Constant or in any event that the gaseous medium shall not be absorbed or rlisappear during the continued` operation oi' the gap.

I have discovercd that if carbon electrodes are in'nersed in a chenically nactive gas that gaps of this character may he operated for long continued perods of time Without any substantial change in gas pressure. I have also found it to be desirablethat an inert gas, such as heli in a substantially pure state be enployed in connection with these carbon electrodes.

In addition to providing carbon electrodes immersed in a monatonic gas, .it is desirahle that the electrodes shall be free from occluded gases and to this end the electrodes prior to' imnersion in the operating gas may be freed 'of gases which may be contained p concentrically with respect to one another;

The specific form of the invention 'shown in the drawing' comprises a hermetically.

sealed receptacle 10 filled with -helium. Enclosed Within the receptacle and imnersed 'in the heliun are two cooperating electrodes 12 and 14 of carbon. The inner electrode is held at opposite ends by steel cups 16 and' 18 which are tied together to clamp the elcctrode in place by a rod 20. The lower cup 18 has a reduced portion 22 received within the electrode member. 14 'and a.

larger skirt portion 24 approximating the diameter of the outer electrode wlich'serves as a shield as hereinafter pointed out. The cup 18 is supported within the receptacle 10 by members 25 which connect the inner face of the portion 24 with the end 26 of the receptacle. The outer and cooperating carbon electrode 12 is enclosed within a cup comprising steel rings 28 and 29 having a band of non-m'agnetic material 30 interposed therebetween and welded thereto in any suitable manner. The carbon electrode cylinder may be conveniently held n the enclosing cup-by a plurality of small pins, as indicated 'at 32, 'and an inturned flange formed on the ring 29. The outer cup member *is connected to the opposite end of the receptacle 10 *by supports 34, as indicated. By virtue of this construction the inner and outer electrode cylinders are securely retained in' concentric relation with respect to one another. A magnetie field is impressed upon the space separating the electrodes by a Permanent magnet, indicated generally at 40, the field being localized in the space opposite the band 30 of non-magnetic material. The inner and outer electrode members are connected with leading-in wires 42 and 44 which may be connected into any desired form of circuit. If a tube of this form is .embodied in a circuit including a source of alternating current and with a magnetic field of correct strength, conduction will take place freely through the gaseous medium when the outer electrode is negative and the tube will act as an insulating medium against conduction in the opposite direction when the inner electrode is negative, thus causing the tube to function as a rectifier. It will be Obvious that a tube of this form may be included in any desired form of circuit and that b a proper design of the tube and the strength of the impressed nagnetie field the tube may be caused to function as a modulator of electric energy as well as a rectifier.

the outer electrode under the influence of the field traverse paths sufficiently long to produce ionization sufficicnt to initiate conduction while electrons traveling from the 4 inner electrode under the infiuence of the field do not traverse paths long enough to produce ionization suficient to initiate con- (luction,

' It has been'explained heretofore that for best results the carbon electrodes should be' substantially free of gas and the gas in which the electrodes are immersed should be helium, neon, or a gas of Similar char acteristics freed from any substantial quantity of impurities in the shape of active gases. Furthermore the carbon electrodes should preferably be in a' pure State, that is free from admixture with clay or Similar impurities, although the form of the carbon may be either the soft graphite of commerce or the harder dense form of carbon commonly employed as are electrodes.

In connection with this inve'ntion it should be understood by those skilled in the art that these carbon electrodes are immersed in a gas through which conduction takes place by virtue of ionization of the gas. In this respect the present form, of apparatus is to be clearly distinguished from apparatus whose conducting properties depend upon the emission of electrons from -an incandescent filament or Similar member or an apparatus having two electrodes between which an electric arc is formed. In the present form of apparatus neither the cathode nor the anode is operated at in'candes-- cence.

While it is preferred to employ the specific construction and arrangement of parts shown and described it will be understood that this construction'and arrangement is not essential except so far as specified in the claims and may be changed or modified llU without departing from the broader features of the invention.

The radial surface of part 24 which exv tends outwardly from the diameter of electrode 14 to the diameter of elctrode 12 intermediate the reentrant stem 26 and the space trical discharge occurs, protects that portion of the tube where. the conductor 22 enters the tube from the electrical discharge .between the two electrodes where the elecand the racliation `of light and vhat therefrom. By making the part 28 nonintegral.

the shield 16- extends lengthwise or longitudinally of the anode 14 along a gap between the depending portion of the shield and thetube 10, the radial dimension of the gap between the dependingportion of the shield and the tube 10 normal to the shield being substantially confined to the mean free path of the electrons in the gas, thereby more efiectually confining the discharge to the interior of the hollow cathode;

The invention having been described, what is elaimed is: p

1. Electrical apparatus comprising spaced electi'odes in a sealed Container contaning gas, the Shortest gap between the electrodes and the gas pressure being correlated to prevent substantial conduction across said gap at potentials which produce gaseous co-nduction along longer 'paths between the elec-` trocles, and that portion of the electrode' which is subjected to bombardment of positive ions being formed of material sufficiently porous notto entrap said gas in substantial degree, whereby the gas pressure is maintained in proper relation to the length of said gap. V

2. Electrical apparatus conprising spaced cathode and anode in a sealed eontainer containing gas, the Shortest gap between the electrodes and the gas pressure being correlated `to prevent substantial conduction across said gap at potentials which produce gaseous conduction along longer paths between the electrodes, and the active surfaceof the cathode being formed of material constituted so as not to entrap 'said gas in substantial degree, whereby the gas pressure is maintained in proper relation to. the length of said gap.

3. Electrical apparatus comprising a sealed Container containing gas, a hollow cathode and an anode presented to the interor surface of the cathode, the .cathode operating below the temperature at which the discharge is dependent upon thermionic emission, said surface being formed of material constituted to prevent permanent entrapment of said gas in substantial degree.

4. Electrical apparatus comprising a sealed Container containing ga, a hollow cat-hode and'an anode presented to the nterior surface of the. cathode, the cathode operating below the temperature at which the' disc harge is dependent upon thermionic emission, the apparatus being' constructed and arranged to confine the bomb-ardment of positive ions substantially to said surface, and said snrface being formed of material constitutedto prevent permanent entrapment of said gas in substantial degree.

5. Electrical apparatus comp-ising asealed Container containing gas, a hollow cathode of the low tempe'atu'e type, and an ano-:le presented to the interior' surface of said cathode, said surface being forn'edof material sufliciently porous at low temperatures to release gas carried into the surface by positive ion bombardment producedby potentials high enough to effect gaseous conduction' between low temperature electrodes.

6. Electrical apparatus comprising spaced cathode and anode of the low temperature type in a sealed container containing gas, the active surface of the cathode being formed of material constituted to prevent permanent entrapment of gas carried into the surface by positive ion bonbardment produced by' potentials high enough to effect gaseous con- -duction between low tenperature electrodes.

7 Electrical apparatus comprising spaced cathode and anode of the loW temperature type in a sealed Container containing gas, the active surface of the cathode being formed of material sufiiciently poro'us at low temperatures to release gas carried into the surface by .positive ion bombardment produced by potentials high enough to eflect gaseous conduction between low temperature elec-` trodes, and meansforconfining the positive 'ion bombardment substantially to said active surface.

8. A gaseous conduction tube containi'g gas and havng a reentrant'. stem a tuhular electrode having ene end directed toward said stem, a member having' an elect-ode sui-- face presented to the Interior of said tublar .electrode, a conductor extending through said stem for conducting current to said surface, and another member having a shielding surface extending transverscly of the axis of said tubular electrode between said 'end of the tubular electrode and said reentrant stem, said shielding srface extending outwarclly from a diameter substantially confined to that of said electrode surface to a diameter at least substantially as great as that of the Opening in the adjacent end of the tubular electrode and extending longitudnallyof said member along a gap sub-' stantially contined to the nean free path of electrons in the gas.

9. A gaseous conduction tube containng gas and having a reentrant stem a hollow' cathode having one end directed toward said stem, a member having an electrode surface presented to the interior of said hollow cathode, a conductor extending through said stem for conducting current'to said surfac'e, .and another member having an annuar metallie surface presented to the space between said hollow eathode and said electrode sui-face intermediate said stem' and said end of the hollow cathode, said annular surface having a radial dimension at least approximately as great as the difference in diameter between said hollow cathode and said electrode sr face and being insula'ted from one of said electrodes by a gap substantially confined to the mean free path of electrons in the gas.

10\. A gaseous conduction tube eontaining gs and haying a reentrant stem ,ra cathode opposte said stem, intermediate said' stem and cathode a member having an electrode surface presented to said cathode, and an other member intermediate said stem and electrode sin-face, the latter member having a surface' extending otwardly from a diameter substantially .confined to that of said electrode surface to a diameter at least substantially as great as'that of said cathode and extending along a gap whose dimension normal to the srface is-`sbstantally conned to the mean free path of electrons Jn the gas. 7

VANNEVAR BUSH. 

